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Does anyone know what this is for? The seller confesses he doesn't.
In small Pentax case, it is a lead with what appears to be a very old-fashioned two-pin UK mains plug* on one end and a specialised lead socket on the other. If it is a Pentax lead, I'm guessing it is to charge a flash unit high voltage battery pack. I can only recall the AF400T pack in that category, but this sort of plug had been phased in the UK ut long before the AF400T was introduced.
* The seller is in the UK, where this design is still used on shaver plugs with transformer isolation, scarily dangerous otherwise.
Pentax vintage power cable in case* | eBay